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. 2024 May 7;15(23):8873-8879.
doi: 10.1039/d4sc01046a. eCollection 2024 Jun 12.

Insulated π-conjugated 2,2'-bipyridine transition-metal complexes: enhanced photoproperties in luminescence and catalysis

Tomohiro Iwai  1 , Shinsuke Abe  1 , Shin-Ya Takizawa  1 , Hiroshi Masai  1   2 , Jun Terao  1
Affiliations

Insulated π-conjugated 2,2'-bipyridine transition-metal complexes: enhanced photoproperties in luminescence and catalysis

Tomohiro Iwai et al. Chem Sci. .

Abstract

2,2'-Bipyridine has been identified as a privileged ligand scaffold for photofunctional transition metal complexes. We herein report on the synthesis and photoproperties of an insulated π-conjugated 2,2'-bipyridine with a linked rotaxane structure consisting of permethylated α-cyclodextrin (PM α-CD) and oligo(p-phenylene ethynylene). The insulated π-conjugated 2,2'-bipyridine exhibited enhanced ligand performance in the solid-state emitting biscyclometalated Ir complexes and visible-light-driven Ni catalysts owing to π-extension and remote steric effects based on the linked rotaxane structure.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Fig. 1
Fig. 1. (a) Conceptual diagrams illustrating issues encountered in π-extended 2,2′-bipyridine ligands. Red dotted lines show π–π and metal–metal interactions, and additional ligation to the metal center. (b) Structure of insulated π-conjugated 2,2′-bipyridine L1 with the linked rotaxane structure end-capped by pivaloyl groups. (c) Optimized molecular structure of L1 calculated using the B3LYP/6-31G(d,p) level.
Scheme 1
Scheme 1. Synthesis and structures of L1–L3.
Fig. 2
Fig. 2. (a) Molecular structure of [Ir(ppy)2(L1)]PF6. (b) Absorption spectra of [Ir(ppy)2(L1)]PF6, [Ir(ppy)2(L3)]PF6, and [Ir(ppy)2(bpy)]PF6 (in CH2Cl2, 1 × 10−5 M). (c) Emission spectra of [Ir(ppy)2(L1)]PF6, [Ir(ppy)2(L3)]PF6, and [Ir(ppy)2(bpy)]PF6 (in CH2Cl2, 1 × 10−6 M, under a N2 atmosphere, excited at 405, 405, 365 nm, respectively). The asterisk indicates the second order of excitation wavelength. (d) Solution (1 × 10−6 M in CH2Cl2) and solid-state luminescence quantum yields (QYs) of [Ir(ppy)2(L1)]PF6 and [Ir(ppy)2(L3)]PF6 (excited at 405 nm under a N2 atmosphere). (e) Schematic of the aggregation suppression of [Ir(ppy)2(L1)]PF6. (f) Natural transition orbitals (NTOs) of [Ir(ppy)2(L3)]+ calculated using the CAM-B3LYP/6-31+G(d,p) (for C, H, N, O) and LANL2DZ (for Ir) levels with the PCM (CH2Cl2) solvation model.
Fig. 3
Fig. 3. (a) Experimental (red solid line) and calculated (black dashed line) UV/Visible spectra of NiCl2·DME/L1 (1 : 1, in DMF) and NiCl2(L3), respectively. A vertical line is assigned to an intraligand charge transfer (ILCT) transition. (b) NTOs of NiCl2(L3) calculated using the CAM-UB3LYP/6-31+G(d,p) (for C, H, N, O, Cl) and LANL2DZ (for Ni) levels with the PCM (DMF) solvation model.
Scheme 2
Scheme 2. Substrate scope in the visible-light-driven Ni-catalyzed C–O coupling with L1. Conditions: aryl bromide (6, 0.1 mmol), HOR′ (4 mmol), NiCl2·DME (1 mol%), L1 (1 mol%), iPr2EtN (0.2 mmol), DMF (0.5 mL), 1,3,5-trimethoxybenzene as an internal standard (0.1 mmol), 427 nm LEDs, 20 h with cooling fans. Determined by 1H NMR analysis using an internal standard. a Isolated yields. b Hydration product 7f was also obtained in 28% NMR yield. c Some unreacted 4-iodobenzonitrile remained in the crude product (83% conversion). Dehaloprotonation product, benzonitrile, was also obtained in 20% NMR yield. d6a (10 mmol), H2O (40 mmol), NiCl2·DME (0.02 mol%), L1 (0.02 mol%), iPr2EtN (20 mmol), DMF (7.5 mL), 427 nm LEDs, 17 h with cooling fans. Complete conversion of 6a was observed. The dehaloprotonation product, benzonitrile, was also formed. e The homocoupling product, [1,1′-biphenyl]-2,2′-dicarbonitrile, was also obtained in 24% NMR yield.
Scheme 3
Scheme 3. Visible-light-driven Ni-catalyzed C–N coupling. Conditions: 4-bromobenzonitrile (6a, 0.1 mmol), H2N-nC8H17 (0.5 mmol), NiCl2·DME (1 mol%), L1 (1 mol%), DABCO (0.2 mmol), DMA (0.5 mL), 1,3,5-trimethoxybenzene as an internal standard (0.1 mmol), 427 nm LEDs, 48 h with cooling fans. Determined by 1H NMR analysis using an internal standard. Isolated yields are shown in parentheses. a Hydration product 7f was also obtained in 13% NMR yield.
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References

    1. For selected reviews on 2,2′-bipyridine, see:

    2. Kaes C. Katz A. Hosseini M. W. Chem. Rev. 2000;10:3553–3590. doi: 10.1021/cr990376z. - DOI - PubMed
    3. Constable E. C. Housecroft C. E. Molecules. 2019;24:3951. doi: 10.3390/molecules24213951. - DOI - PMC - PubMed
    1. Ward M. D. White C. M. Barigelletti F. Armaroli N. Calogero G. Flamigni L. Coord. Chem. Rev. 1998;171:481–488. doi: 10.1016/S0010-8545(98)90071-6. - DOI
    1. Munegowda M. A. Manalac A. Weersink M. McFarland S. A. Lilge L. Coord. Chem. Rev. 2022;470:214712. doi: 10.1016/j.ccr.2022.214712. - DOI - PMC - PubMed
    2. Teets T. S. and Wu Y., Organometallic Photosensitizers, In Comprehensive Organometallic Chemistry IV, ed. G. Parkin, K. Meyer and D. O'hare, Elsevier, Oxford, UK, 2022, pp. 284–338
    1. Teegardin K. Day J. I. Chan J. Weaver J. Org. Process Res. Dev. 2016;20:1156–1163. doi: 10.1021/acs.oprd.6b00101. - DOI - PMC - PubMed
    1. Joshi H. S. Jamshidi R. Tor Y. Angew. Chem., Int. Ed. 1999;38:2721–2725. doi: 10.1002/(SICI)1521-3773(19990917)38:18<2721::AID-ANIE2721>3.0.CO;2-5. - DOI - PubMed